Key works of Aristotle:

• Categories

• Nicomachean Ethics

• De Anima

• Metaphysics (esp. Books I, II, IV, VII-IX, XI, XII)

• Posterior Analytics

Key works of Aquinas:

• De Ente et Essentia

• Commentary on Boethius’ De Trinitate

• Summa Contra Gentiles

• De Potentia Dei, q. 7

• Disputed Questions on the Soul

• Summa Theologiae

• Commentary on the Gospel of St. John

Moderns:

• Fr. Stephen Brock, The Philosophy of St. Thomas Aquinas: A Sketch

• Edward Feser, Aquinas and Introduction to Scholastic Metaphysics

• Réginald Garrigou-Lagrange, OP Reality and Grace (all chapters available on EWTN’s website)

• Lawrence Dewan, OP Form and Being

• Étienne Gilson, Thomism: The Philosophy of Thomas Aquinas, 5th edition (1948 edition)

• Benedict Ashley, OP The Way toward Wisdom

• John Wippel, The Metaphysical Thought of Thomas Aquinas

• Gilles Emery, OP The Trinitarian Theology of Thomas Aquinas

• Jean-Pierre Torrell, OP St. Thomas Aquinas, Vol. 2: Spiritual Master, Encyclopédie Jésus le Christ chez saint Thomas d'Aquin, and Le Christ en ses mystères: La vie et l'oeuvre de Jésus selon saint Thomas d'Aquin (two volumes)

• Steven Jensen, Knowing the Natural Law: From Precepts and Inclinations to Deriving Oughts

• Servais-Théodore Pinckaers, OP The Sources of Christian Ethics

• Lawrence Feingold, St. Thomas Aquinas and the Natural Desire to See God

• Steven Long, The Teleological Grammar of the Moral Act

• Alasdair MacIntyre, Three Rival Versions of Moral Inquiry

• Thomas Joseph White, OP The Incarnate Lord

• Jean-Hervé Nicolas, OP Synthèse dogmatique 

• Charles Cardinal Journet, L'Eglise du Verbe incarné (several volumes, masterpiece of Thomist ecclesiology—here's volume one) and The Mass: The Presence of the Sacrifice of the Cross

• Benoît-Dominique de La Soujeole, OP Introduction to the Mystery of the Church

• Colman O’Neill, OP: Several helpful works on Aquinas’ sacramental theology

Journals:

• Nova et Vetera (English edition)

• The Thomist

• Revue Thomiste